I use it on an iPad 4, and I bought it for about $1. It's slow to work on D800 RAWs (as i'd expect), but slow to open my Fuji X20 RAWs too. Adjustment sliders use application-specific units of measurement which don't translate to other packages as far as i'm aware. Highlights and shadows seem to clip more easily than i'd expect my files to, and sometimes appying too many adjustments or brushes seem to cancel each other out.
Don't expect too much, use it for the odd fun bit of editing or checking out your photos before you can get them back to your workstation, and it will be a satisfactory bit of software. Don't expect to do finished pieces with it; and if you do, expect it to take a long time and not look as good as you'd hoped.